Let's say we have three search results, good, average and bad, displayed on one result per page in that order. The user is happy, Google is unhappy as there is no motivation for the site owner of the best search result to pay Google for their listing. The only way Google gets money is if it enables the result order to be modified, i.e. the owners of the average or poor sites to disproportionately effect their listing prominence by appearing on page 1. Google do this by allowing paid adverts. Bad or average search results thus get disproportionately high prominence in the listing with the knock on effect that the owner of the best search result now has motivation to pay Google to regain their primary listing. And even further, if the site owner of the best search results now has to pay Google for the prominence of their listing why waste money on continuing to provide the best results? The user is unhappy, Google is happy.